On 02/03/2014 08:30 PM, Stan Hoeppner wrote: > On 2/3/2014 8:42 AM, Phillip Susi wrote: > >> On 2/3/2014 1:34 AM, Stan Hoeppner wrote: >>> Please reread my statement above. Now let me restate that as: >>> >>> Measuring disk throughput when writing through the buffer cache >>> isn't a measurement of disk throughput as much as it is a >>> measurement of cache throughput. Thus, such measurements do not >>> demonstrate actual disk throughput. >>> >>> Do you disagree? >> Yes, I do because cache throughput is >>>> disk throughput. > It is because buffer cache throughput is greater that measurements of > disk throughput are not accurate. If one issues a sync after writing > through buffer cache the measured throughput should be fairly close. > But without issuing a sync you're measuring buffer cache throughput. > > Thus, as I said previously, it is better to do parallel O_DIRECT writes > or use AIO with O_DIRECT for testing disk throughput as one doesn't have > to worry about these buffer cache issues. > Perhaps Phillip is doing the obvious and only measuring throughput after the cache is full. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
